Porphyrins and Quantum Dots as Photodynamic Therapy Agents
There are several different projects that students have been investigating. The first project involves the synthesis and characterization of porphyrins and their coupling with quantum dot (QD) materials. QD’s are nanoparticles that have unique fluorescent behavior. Porphyrins have fluorescent properties themselves, and some derivatives have been used in Photodynamic Therapy (PDT). Metalloporphyrins have been shown to be tumor specific and thus have potential as possible tumor therapy agents. It has been recently demonstrated that the synthesis of these neutral porphyrins containing poly-alcohol functionalities to achieve water-solubility can be carried out (Figure 1). This project examines the synthesis, purification and characterization of these QD-porphyrin nanoparticles and their cellular uptake. This research is funded by a J. D. Patterson Grant.
The second project entails the synthesis, characterization, and relaxivity of target-specific MRI (magnetic resonance imaging) contrast agents. Although MRI contrast media have been available for some time, designing MRI contrast media that is organ specific has been difficult, particularly designing contrast agents that cross the blood brain barrier. This project involves the synthesis of a novel gadolinium MRI contrast media for brain imaging.
The Role of Retinoblastoma Family Proteins in the Differentiation of Pre-Adipocytes
My research interests center on the molecular mechanisms involved in the permanent exit of cells from the cell cycle as they terminally differentiate. Cells that previously proliferated in response to external signals now respond to those same signals in a different way. What changes in the cell to alter its response?
The major project in my lab looks at this question using the terminal differentiation of pre-adipocytes as a model. Pre-adipocytes proliferate rapidly and can be cultured in the lab. When they are contact inhibited they can be treated with a cocktail of hormones and will respond by differentiating. Over the course of the next few days they express fat cell proteins, produce lipid droplets and turn into adipocytes. During this time many of the cells divide once or twice but when this period is past they are post-mitotic- they never divide again.
My lab is working on the roles of the Retinoblastoma family proteins p107, p130 and pRB during the early stages of this process. We are ‘knocking down’ the expression of each of these proteins individually and in combinations to determine the effect on differentiation. Our experiments utilize cell culture, protein techniques (electrophoresis, Western blotting, etc.), cell biology methods (virus infection, microscopy and cell staining with dyes and antibodies) and molecular biology techniques (transfection, electroporation, making plasmids, PCR, etc.) as required by the particular experiment being done.
The analysis of bis-phenol A in water samples using solid-matrix fluorescence spectroscopy
Bis-phenol A (BPA) is used in the production of epoxy resins and polycarbonate plastics and frequently remains in these materials. In vitro and in vivo experiments show that BPA exhibits weak estrogenic activity by binding to and activating estrogen receptors. Suspected effects of modified endocrine functions may be reduced fertility, altered development, and cancer in estrogen-sensitive tissues. Infants and children are particularly at risk due to their still developing neurological and endocrine systems and the fact that their ability to detoxify and eliminate substances such as BPA is immature. This concern led to a change in the plastic used for baby bottles and other containers, which removes BPA from the plastic, allowing manufacturer’s to claim their products are “BPA free”. Despite this reduction of BPA in current food packaging, BPA is still present in our environment due to BPA-containing waste in landfills or ocean trash. The environmental sources, though at low levels, are a particular concern for the exposure of infants and children and also for aquatic organisms.
BPA is a fluorescent compound, which means following excitation, it will emit radiation at a longer wavelength than the exciting wavelength. BPA is excited at ~280 nm and emits and ~310nm. This emitted light can be measured and correlated to the concentration of BPA present in a sample. Fluorescence is a very sensitive and selective technique, which makes it possible to determine very low concentrations BPA with fewer concerns about outside interferences compared to absorption spectroscopy. However, the fluorescence intensity can also be decreased (quenched) by collisions within a solution. By preparing a solid sample, such as a sugar glass, containing the sample it is possible to detect lower concentrations of BPA compared to a sample in solution.
The goals of this project are to obtain fluorescence data for BPA using sugar glasses as a solid matrix and to explore the effects of temperature and time on the leaching of BPA-containing materials into water samples.
The Life and Works of Frederick Sanger, Nobel Laureate in Chemistry 1958, Nobel Laureate in Chemistry 1980
Dr. Frederick Sanger was awarded the Nobel Prize in Chemistry in 1958 for his work in determining the structure of insulin, the first protein molecule sequenced. He became only the third two-time recipient of the Nobel Prize when he shared the 1980 Nobel Prize in Chemistry for developing techniques for sequencing DNA molecules. Dr. Sanger worked first in the Biochemistry Department at Cambridge University in England. Then he worked at the Medical Research Council Laboratory of Molecular Biology in Cambridge. I have interviewed Dr. Sanger and many of his colleagues and family members. I continue research to prepare articles for the Bulletin for the History of Chemistry and to write a biography of Frederick Sanger. This research is funded by a J. D. Patterson Grant.
Nitroanisole Detoxification by CYP2E1
The prevalence of complex non-hyperbolic reaction kinetics and impact on metabolism of xenobiotic compounds has been relatively unexplored for CYP2E1, a cytochrome P450. Inadequate knowledge of kinetic parameters compromises the interpretation and prediction of the consequences of P450-mediated biotransformations, and thus impact effective drug design, food safety guidelines, and environmental regulations. Nitroanisoles are environmental pollutants whose toxic potential depends on the efficiency of biological processes.
While xanthine oxidase activates nitroanisoles to mutagenic compounds, P450s, most notably CYP2E1, oxidize nitroanisoles to non-toxic products poised for elimination from the body, thereby committing nitroanisoles to detoxification. Thus, the efficiency of CYP2E1 metabolism toward nitroanisoles is a potentially important determinant for risk posed by exposure to those pollutants. Based on our previous work and others, we hypothesize that the contribution of CYP2E1 to nitroanisole detoxification depends on the occupancy of an effector site by nitroanisoles or the corresponding metabolites. Further studies are necessary to assess the specificity of the active and effector sites for molecules and corresponding impact on reaction kinetics.
The primary objective of our work at OBU is to construct computer models for CYP2E1 complexes with substrates and effectors to predict non-hyperbolic reaction kinetics. We will use the CYP2E1 crystal structure to create liganded complexes computationally through two different docking approaches, and thus determine complex stoichiometry and contact residues for bound ligands. Our work is in collaboration with Dr. Grover Miller in the Biochemistry Department at UAMS.